Noradrenalin, also known as norepinephrine, is a substance belonging to the catecholamine group, derived from the amino acid tyrosine. It is synthesized and released throughout the body, serving as a rapid messenger that mobilizes and regulates various physiological processes. Its presence is fundamental to both immediate survival mechanisms and everyday mental and physical functioning.
Noradrenalin’s Dual Identity
Noradrenalin serves as both a neurotransmitter and a hormone. As a neurotransmitter, it is produced within the central nervous system, primarily in the locus coeruleus, a region situated in the brainstem. Here, it transmits signals between nerve cells, influencing brain activity and cognitive functions.
As a hormone, noradrenalin is released directly into the bloodstream by the adrenal glands, which sit atop the kidneys. The adrenal medulla produces and secretes it alongside epinephrine (adrenaline). Circulating as a hormone, noradrenalin affects distant tissues and organs, leading to widespread physiological changes.
The Acute Stress Response
Noradrenalin is integrated into the “fight-or-flight” response, activated by the sympathetic nervous system. When the brain perceives a threat, a surge of noradrenalin is released, preparing the body for intense physical action. It acts on heart receptors, increasing the heart rate and strengthening contraction, thereby boosting cardiac output.
It also triggers widespread vasoconstriction, the narrowing of blood vessels, primarily in areas less vital for survival like the skin and digestive system. This action serves to significantly raise blood pressure and redirect a larger volume of blood toward the skeletal muscles, lungs, and brain. Furthermore, noradrenalin stimulates the breakdown of energy stores, releasing glucose into the bloodstream to provide immediate fuel for responding muscles.
Regulating Baseline Functions
Beyond acute threat responses, noradrenalin plays a role in maintaining internal stability and cognitive performance. It continuously acts within the central nervous system to regulate states of wakefulness and arousal. This ongoing signaling helps transition the brain from a sleeping state to a fully alert state, facilitating the natural sleep-wake cycle.
The system originating in the locus coeruleus projects widely throughout the brain, modulating functions essential for daily life, such as focus and attention. Intermediate levels of noradrenalin are associated with optimal cognitive performance, enhancing sensory signal detection and concentration. It helps stabilize mood and contributes to memory formation and retrieval. This background activity ensures that the body’s baseline blood pressure is maintained.
When Noradrenalin Levels Fluctuate
Dysregulation of noradrenalin levels is associated with several medical and psychological conditions. Chronically high levels can lead to symptoms like anxiety, hypertension, and a persistently high heart rate, which stresses the cardiovascular system. This hypervigilant state can manifest as nervousness, difficulty sleeping, and poor physical health outcomes over time.
Conversely, insufficient noradrenalin signaling in the brain is linked to fatigue, poor concentration, and low energy, often seen in conditions like depression and attention deficit hyperactivity disorder (ADHD). Certain medications, such as some antidepressants, work by increasing noradrenalin availability to alleviate these symptoms. In critical care settings, noradrenalin is used clinically as a vasopressor drug to treat dangerously low blood pressure, particularly in cases of septic shock. Its potent vasoconstrictive properties rapidly increase systemic vascular resistance to restore adequate blood pressure.